One can only speculate, but it would appear it's an attempt to compare the ordeal of the Chilean miners to Hanoi Hilton prisoners of war, perhaps inferring the POW's are more heroic than the miners due to the length of their captivity.

It's kind of an apples-to-oranges comparison though. The miners were, en masse, victims of a very unfortunate accident, and not imprisoned at gunpoint due to being captured by enemy combatants while at war. But, I think it could be argued that the miners were heroic in whatever actions they may have taken to survive their ordeal, just as did the Hanoi Hilton POW's. Totally different types of ordeals, however.